Glass Transparency Seems Dark
In the Principled BSDF shader, the default Base Color is a very light gray. To make sure the surface absorbs no light, set the Base Color to pure white.
(If you are using the Glass BSDF shader, make sure its color is white as well)
I'm assuming you have a simple 1-node shader setup. If you have something more complex, it is possible that the other materials are affecting the transparency color as well. Make sure you aren't mixing the material with a darker material in a mix node or similar.
Also check that there is no volume absorption shader set on the material. This can cause it to appear darker as well.